Sep. 24, 2013 — Noise from traffic and artificial night lighting cause birds in the city centre to become active up to five hours earlier in the morning than birds in more natural areas. These were the findings from an investigation conducted on 400 blackbirds in Leipzig by the interdisciplinary research group "Loss of the Night." Scientists from the Helmholtz Centre for Environmental Research (UFZ) reported in the open-access journal PLOS ONE that these findings showed how ambient noise and light pollution caused by humans have significant effects on the behavioural patterns of city blackbirds, affecting their natural cycles.
The scientists choose the Common Blackbird (Turdus merula) as the model organism for the investigation. This medium sized thrush was originally a forest-dweller, but since the early 19th Century it has become well-adapted to the conditions of cities, where it is now a common resident that is easily identified by its very distinct birdsong. In spring of 2011 and 2012, both over 15 weeks, data on the behaviour of blackbirds were recorded and analysed in the 215-hectar study area in Leipzig. The study area covered an urban gradient of 3km stretching from the city centre through the Clara Zetkin Park to the floodplain forest.
For biologist Anja Ruß and some hard-working students the field work involved numerous nightshifts of patrolling blackbird territories between 1:30am and sunrise to record the birdsong behaviour of male blackbirds in order to locate and record the behavioural patterns of over 400 individuals. In addition, the scientists used data from official statistics for calculations on the distribution of artificial lighting and noise levels of the surrounding environment. Due to the artificial lighting of roads it was much brighter at night in the green areas close to the city ring road than in the floodplain forest. "The brighter the night, the earlier the blackbirds started their dawn song. We found this linear relationship for low levels of artificial night light but it seemed to reach a threshold. If this threshold is exceeded, an increase in light intensity will not lead to an even earlier onset of dawn song," reports Anja Ruß from the UFZ.